Hydrodemolition techniques are being used for the refurbishment contract on Montreal's Highway 720 Ville Marie Tunnel, a key arterial east-west highway across the city. Delivery of a new aquajet robot is being used for the first in the region to complete the work more efficiently and to better quality than mechanical methods.

1000 bar hydrodemolition pressure in the live traffic tunnel

Canada's infrastructure and general contractor, GTS, has taken delivery of the latest generation HVD Evolution robot from Sweden's Aquajet Systems AB, to use hydrodemolition techniques on its contract in Montreal's Vile Marie Tunnel.

Purpose-ordered through local distributor Pompaction, it is the first HVD Evolution hydrodemolition machine in Quebec and the Maritime Provinces.

Hydrodemolition ensures no rebar damage, minimises the risk of good concrete removal, eliminates dust and airborne crystalline silica, and provides a superior surface for effective bonding of the new repair concrete.

It is also a substantially faster technique than mechanical removal methods and is also considerably less labour intensive.

Tunnel application
The 3km long Ville Marie Tunnel was opened in the mid 1970s and features a mix of 3, 4 or 5 lanes along its route. As a key arterial east-west highway across the city and more than 100,000 vehicle movements a day, it is essential that traffic restrictions during the refurbishment works are minimised.

Montreal's Ville Marie Tunnel

The GTS contract involves replacing about 1km of concrete on both sides of the eastern portals directly below the Montreal Palais des Congres and close to the Downtown Jacques Cartier Bridge.

Concrete is being removed to a depth of 12mm to expose the old rebar. An additional 100mm and new rebar for further strength is being added for a total thickness of 225mm.

In replacing the old concrete, the opportunity is also being taken to reroute electrical and telecoms cables and fibre optics into a common conduit and install new improved lighting in the tunnel.

A chequered pattern of concrete removal was specified, taking into account structural design loadings of the tunnel wall. Alternate sections measuring 2.4m x 5m height along the bottom level and 0–1 m along the upper level at the portal, are undertaken at a time.

Working at 15m high

Close to the portal exit two areas over a length of 15m were found to be particularly unsound and in very poor condition. The client therefore specified that for safety of the workforce, the entire section should be removed in a single operation.

GTS had initially allocated two shifts a day for the hydrodemolition process but such is the speed and efficiency of the Aqua Cutter Evolution that the contractor is working just a single shift per day for the operation.

Project Manager, Michel Francoeur had previous experience with hydrodemolition techniques using a standard Aqua Cutter robot rented from Toronto for a bridge deck slab project in Montreal. "We had been very impressed with the performance and quality of work and recognised the potential for this tunnel project," he said, adding, "on winning this contract we took delivery of the new unit together with the a PP700 power pack –and we have not been disappointed."

Extra layer of rebar for added strength

GTS started work on the contract in mid-August last year (2009) with an October 2010 completion date, expecting to finish work along the slow lane tunnel wall by March and operations then switching to the fast lane side of the tunnel, closing the outside lane.

Operating in 'live' traffic conditions, with very heavy traffic flows, and working at heights of up to 15m, it was essential that the contractor protected both its workforce and the passing traffic from falling debris.

As a result the robot is installed behind a protected frame and positioned on a telescopic handler for ease of access for the extended height operations. The Aqua Cutter is thought to be the only robot in the world that is able to operate at heights of up to 15m. This was a key factor in GTS purchasing the Aquajet system.

Protecting workers and traffic from pressure and debris

Operating at 1000 bar, the Aquajet hydrodemolition system uses a water flow rate of 260 litres/min and is achieving a deteriorated concrete removal rate of up to 1.5m3/h.

"Without the Aqua Cutter GTS would have used conventional jackhammers to remove the concrete," said Francoeur.

Using the Aqua Cutter removes damaged concrete at the speed of several hydraulic jackhammers and more than 25 times faster than hand held hammers.

It also requires just one or two operatives compared with one worker per hammer. Hydrodemolition also eliminates the risk of white finger, complying with European work practises.

Add your comment

Thank you for taking the time to share your thoughts and comments. You share in the wider tunnelling community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language professional.